The conventional approach in cardiac resynchronization therapy (CRT) involves pacing from an electrode provided close to the right ventricular (RV) apex, an electrode on a transvenous left ventricular (LV) lead, typically in the lateral or postero-lateral vein, and optionally an electrode in the right atrium (RA).
In such a case, the optimal interventricular (VV) delay between RV and LV pacing pulses and the optimal atrioventricular (AV) delay between atrial and ventricular pacing need to be determined. Several prior art solutions to such an optimization problem have been suggested. U.S. Pat. No. 5,514,163 optimizes an AV delay based on far field R wave sense (FFRS) duration. U.S. Pat. Nos. 6,751,504 and 6,804,555 use the width of the QRS in order to set optimal VV delays. In another document, U.S. Pat. No. 7,848,807, optimal AV and VV delays are determined based on the width of a P wave from a sensed far-field electrocardiogram.
Recent studies have suggested that biventricular pacing from two LV sites results in an improved clinical outcome in CRT patients, likely due to improved hemodynamic response from dual-LV pacing, in comparison with conventional biventricular pacing. However, the number of possibilities to select electrodes and to set delays between electrodes increase dramatically with increasing number of electrodes required for having multiple pacing sites within a ventricle.
For instance, assume a case with two independent LV pacing pulses and that there are ten possible stimulation vectors to choose from for each pulse. In such a case, there are two separate VV delays (or expressed differently one VV delay and one intraventricular delay) to be tested. Further assume, that the VV delay could be of one out of ten defined values and the intraventricular delay could be one out of 16 different values. The two ventricles can be paced in two different ways: RV first or LV first. This ends up with 10×10×10×16×2=32,000 different combinations. It is obvious that it is not possible in real applications to test each such combination in order to find the optimal VV and intraventricular delays. Efficient optimization procedures are thereby needed.
U.S. Pat. No. 6,522,923 is directed towards finding optimal AV and VV delays by testing a set of randomly selected AV and VV delays within a defined AV/VV space. The most optimal of the tested AV and VV combinations is found and a new set of randomly selected AV and VV delays are tested within a smaller AV/VV space centered at the most optimal AV/VV-combination. This procedure is repeated multiple times with ever smaller AV/VV spaces until a final optimal combination of AV and VV delays is found.
There is, however, still a need for efficient techniques to determine optimal VV delays for a system having multiple pacing sites.